Data storage media are commonly used for storage and retrieval of data, and come in many forms, such as magnetic tape, magnetic disks, optical tape, optical disks, holographic disks, cards or tape, and the like. Magnetic tape media remains an economical medium for storing large amounts of data. For example, magnetic tape cartridges, or large spools of magnetic tape are often used to back-up large amounts of data for large computing centers. Magnetic tape cartridges also find application in the backup of data stored on smaller computers such as desktop or laptop computers.
In magnetic tape, data is typically stored as magnetic signals that are magnetically recorded on the medium surface. The data stored on the magnetic tape is often organized along “data tracks,” and read/write heads are positioned relative to the data tracks to write data to the tracks or read data from the tracks. Other types of data storage tape include optical tape, magneto-optic tape, holographic tape, and the like.
Data storage media typically include a section of data set aside as a tape directory, e.g., Media Information Repository (MIR) or Format Identification Data (FID), to store information relative to the tape format and/or data stored on the tape. For example, in data storage tape the directory may include tape information such as the data block number at the start position for every track. The tape directory may also include information regarding the data content and location on the track. Tape directory information may need to be accessed to properly read and write data to the tape.
Data storage on magnetic media is not infallible. For example, a data storage tape may become damaged or dirty, making data on the data storage tape unreadable. The magnetic properties of the media can also degrade to making data unreadable. In order to maintain data integrity in the event data becomes unreadable, many data storage systems include error correcting code (ECC). For example, one simplistic form of error correcting code requires adding a single bit to a portion of data to signify whether the sum of the data bits is odd (1) or even (0). For example, in the byte “1 0 0 0X0 1 1”, the first seven bits may represent data with “X” being an unreadable bit, and the last “1” is the ECC. Simple logic can be used to determine X. Specifically, 1+0+0+0+X+0+1=odd, therefore X=1. More complex forms of ECC are also available, such as Reed-Solomon encoding.